It is known to use germanium as a substrate material for epitaxial growth of III–V materials. Germanium is a substrate of choice the space solar cell industry for GaAs and GaInP/GaAs substrates. In this application, germanium substrate is used either with an active semiconductor junction inside of the Germanium substrate or without an active junction in Germanium.
Devices that use these III–V materials are typically photonic devices such as solar cells, light emitting diodes (“LEDs”), photo detectors, or electronic devices such as transistors and diodes. To produce such devices, commonly III–V substrates are used for epitaxial growth of high-quality layers that with further chemical and physical processing will constitute these devices. Usually the substrate for the epitaxial growth of high quality epitaxial films has to have lattice matching with the layers that are to form a device.
Metallo-Organic Vapor Phase Epitaxy (MOVPE) is a technique of choice for the formation of many types of epitaxial III–V semiconductor layers. MOVPE is also often know as MOCVD (Metallo-Organic Chemical Vapor Deposition) or OMVPE (Organo-Metallic Vapor Phase Epitaxy).
The existence of intrinsic substrates in the “semi-insulating” form enabled high-frequency operation of these microelectronic and optoelectronic devices. The disadvantage of these intrinsic substrates is their high cost of use and manufacture. These substrates cannot be used to the device formation in the substrate itself. The substrate is inherently passive.
Optoelectronic properties of Germanium have also been combined with III–V devices to produce multifunction solar cells. In this respect, the optical and semiconductor properties of Germanium have been combined with the optical properties of III–V materials to efficiently convert solar energy into electricity. To date, it is believed that this technology has been limited to photovoltaic applications.
One problem with currently available technology is the cost of using a conventional substrate such as GaAs and InP in microelectronic devices. This cost has effectively prevented III–V devices from being used in many different markets and applications.
Another problem with currently available technology is that growth substrates have typically been limited to III–V materials for use as templates to ensure high quality of the epitaxial III–V films.
It would be highly desired to combine the material and electrical properties of germanium, which is a group IV semiconductor, with material and electrical properties of III–V compounds in such a way as to create electronic devices in epitaxialy grown III–V films integrated with optical and electronic devices in germanium.